Oscilloscopes are tools that engineers often use to measure signals from electronic devices. Oscilloscopes may be used to view analog or digital waveforms in a circuit, for example. Circuit signals may be tapped using voltage or current probes that are coupled to an oscilloscope.
When received at an oscilloscope input, a waveform is typically conditioned by various filters and amplifiers. In a typical digital oscilloscope, the waveform is sampled and converted to a digital representation, and then either displayed or stored in a memory device.
Prior to conversion from an analog waveform to a digital representation, input signals may be, for example, buffered, amplified, and/or level shifted by signal conditioning circuitry. Some signal conditioning circuits may have a relatively high impedance input to minimize loading of the input signal. After being conditioned, the input signal may be sampled. For example, a track and hold circuit may be used to sample a signal by capturing a signal voltage on a capacitor.
Achieving high bandwidth in a digital oscilloscope generally involves fast sampling. Accordingly, some signal conditioning circuits may include transistor circuits to facilitate rapid charging of a capacitor in the sampling circuit.
At certain signal frequencies, transistor circuits can exhibit a significant “thermal tail” effect due to temperature changes that may result from changes in the power dissipation. In the signal conditioning circuitry of a digital oscilloscope, for example, thermal tail effects can distort some signals before the signals are sampled. As such, thermal tails can result in sampled waveforms that include a thermal tail component in addition to features of the original input signal waveform.